Numerous circuits and systems employ pulse signals to initiate, activate, or otherwise control circuit and/or system functions. Most often the pulse signals are required to be within specified limits as to duration, duty cycle, and the like. In telecommunications systems, for example, pulse signals are employed for numerous purposes. of particular interest are supervisory signals employed in signaling systems. Supervisory signals include, among others, operate and release control signals and dial pulses; it being important that the operate and release functions, although used for initiating dial pulse correction, not interfere with the dial pulse correction function.
One characteristic of dial pulses which is of particular importance is the so-called break interval and its percentage of the overall dial pulse interval, i.e., break plus make intervals. As is known, dial pulses may be received which vary in repetition rate from some minimum, for example, 7.5 pulses per second (pps) to some maximum, for example, 12.5 pps. It is important in certain system applications that the percentage of the individual dial pulse break interval be substantially constant relative to the overall dial pulse interval over a desired range of incoming dial pulse rates.
A number of arrangements are known which tend to generate dial pulse signals corrected to a substantially constant percentage break interval over a range of incoming dial pulse rates. The prior known arrangements include both analog and digital implementations. The analog arrangements typically include a plurality of analog resistor/capacitor (RC) timer circuits to realize desired functions. In one known analog arrangement a tandem arrangement of an operate delay timer, release delay timer, make timer and break timer is employed in conjunction with output logic elements to obtain the desired constant percent break pulse correction. In this arrangement the RC time constant of the break timer is controlled by the make timer in response to the incoming dial pulses to yield the desired break interval ratio to the overall pulse interval of make plus break intervals.
Another analog implementation has employed so-called integrating timer circuits of a type disclosed in U.S. Pat. No. 4,001,698 issued to R. R. Allred on Jan. 4, 1977 for the operate delay timer, release delay timer, make timer and break timer.
One problem common to the analog implementations is that they employ capacitors and other analog circuit components. Circuits which use capacitors and other analog circuit components are not readily implemented in integrated form. Indeed, with the advent of large-scale integration it becomes highly desirable to implement pulse repeating and correcting circuits by utilizing digital techniques.
Additionally, prior analog circuits have tended to be deficient because of their sensitivity to incoming spurious signal conditions, for example, noise and the like, thereby affecting their accuracy and dependability. A condition of particular concern arises under noisy incoming signal conditions. Under the noisy signal conditions it has been demonstrated that prior analog constant-percent break interval pulse correctors have erroneously generated a train of output dial pulses. The generation of unwanted dial pulse signals has been designated "dial pulse correcting forever" phenomenon and is extremely undesirable.
A constant-percent break dial pulse correction circuit implemented by employing digital techniques is disclosed in U.S. Pat. No. 3,700,821 issued to B. R. Savage on Oct. 24, 1972. In this arrangement digital up/down counters and associated logic elements are employed to realize the operate and release delay timer functions while digital counters and associated logic elements are employed to realize the make and break time functions. This arrangement is also believed to be sensitive to incoming spurious signal conditions, specifically noise, thereby being susceptible to generating erroneously a train of output dial pulses known as "dial pulse correcting forever". The dial pulse correcting forever phenomenon is possibly initiated in response to incoming noise signals because of interaction between the operate and release delay timers, the up/down counting arrangement of the operate timer, and interaction between the operate timer and the pulse correction make and break timers. Again, erroneous generation of output dial pulses is extremely undesirable and should be avoided.